Alloy steel and method



w. c. CLARKE, JR 3,069,257

ALLOY STEEL. AND METHOD Dec. 18, 1962 2 Sheets-Shut 1 Filed June 2. 1960 bens W//l/'am 6. C/ar/rq/r. BY j 7L /5 ATTORNEY 'smb-ss, Ps/

SQG max u n w n w Dec. 1s, 1962 ALLOY STEEL Filed 'June 2, 1960 RUPTURE STRESS, PS/ x /000 FIG. 2

W. C. CLARKE, JR

AND METHOD 2 Sheets-Sheet 2 CURVE FUR 4/2-M COMPARE D W/ Th' MSTER RUPTURE CURL/ES FOR 422 A/vo 42e-Ml ,Lf/.5' ATTORNEY william \.c. Clarke, Jr.,

. 3,069,251 ALLOY STEEL AND METHOD Armyco Steel Corporation, a corporation of Ohio FiledJune 2, 1960, Ser. No. 33,579 'f f "d 5 Claims. (Cl. 75-126) low in cost and relatively simple both in melting and in conversion to sheet, strip, bars, rods and the like; which steel displays superior mechanical properties at room temperatures and at elevated temperatures, as well, over prolonged and repeated service under the many varying conditions encountered in actual practical use;

All the foregoing, together with many highly practical advantages, attend the practice of my invention, these being obvious in part and in part pointed out more fully in the following disclosure.

Accordingly, my invention resides in the combination of component metals and constituents, particularly their relationship to and with each other, and in the proportioning thereof in the nal alloy'obtained therefrom, and in the various procedural and manipulative steps and the relation of each of the same to one or more of the others, the scope of the applicaiton of all of which is more fully set forth in the claims at the end of this disclosure.

In the accompanying drawings:

FIG. 1 graphically illustrates the stress rupture properties of the steel of my invention as a function of temperature in comparisio'n with those of a similar steel of the prior art, and

FIG. 2 illustrates the stress rupture properties of my steel in comparison with published information on two steels of the prior art, one being that illustrated in FIG. 1.

As conducive to a more thorough understanding of my invention, it may be noted that where temperatures of application here exceeded about 1000' F., recourse has been hadto the austenitic chromiumnickel steels. However, this is not desirable in many instances 'because of the higher cost of such steels and their high coetiicient of expansion and low' damping capacity. Attention therefore has -been turned to improving the straight chromium grades. Y

Practical ditliculty has lbeen encountered in improving the straight chromium grades, however, because ordinarily such steels do not display requ-isite and desired mechanical'strength when subjected to high `temperature operation, i.e., to temperatures within the approximate range of 1000 F. to 1200 F. In those instances where in fact acceptable strength was initially displayed, that`strength rapidly suffered under prolonged operation at high temperatures, especially where the high temperature duty is repeated or cyclical in nature. dustry has directed much attention towards producing a high temperature steel. But the efforts made have encountered many practical difliculties.

IIllustratively, it has been proposed to modify the known 422 type chromium-nickel steel, with a view to increasing the hot strength valuesthereof. The type 422 typically analyzes: .28% carbon, 11.7% chromium, .70% nickel, .65% manganese, .36% silicon, .95% molybdenum, .93% tungsten, .25 vanadium, and remainder iron.

In ank effort to increase the high temperature strength of the type 422 it has been proposed to add substantial quantities of tungsten, molybdenum and vanadium. The modified type 422-M is of substantially greater molybdenum rand tungsten content. A typical steel of the Baltimore, Md., asslgnor to N United States Patent O 3,069,251 Patented Dec. 18, 1962 ceg 422-,M analyzes:v.28% carbon, v:11.8% chromium, .20% nickel, .84% manganese, .24% silicon, 2.24% `molybdenum, 1.72% tungsten, .50% vanadium, and remainder tron.

While the additives have contributed somewhat to the high temperature strength of the resulting alloy (type 422-M), certain practical diticulties are encountered n the multiple processing involved. As well, the added metals are themselves quite expensive. Moreover, and even with such additives included, the modited 422 steel is not entirely satisfactory in that the strength under high temperature operating conditions does not fully respond to industry requirements. a

Thus, while some progress has been observed in accomplishing the sought-for objectives, nevertheless a fully satisfactory and completely acceptable steel, `responding to the foregoing basic requirements, has not yet been produced. Much work remains to be done in this regard.

An object of my invention, therefore, is to overcome and avoid in substantial respect, the many disadvantages heretofore confronting the industry and at the same time to produce in simple, direct and certain manner, la stainless steel which, through etective control of the usual components present, displays appreciable increase inthe. 2.5 strength under enduring, prolonged and repeated high temperature operation, all this being brought aboutwith out necessity for recourse to further alloying additives, and all at minimum expense.

Referring now to the practice of my invention I produce 3.0 a modified 12% chromium alloy steel, more particularly a modiication of the well-known commercial type 410. The specification for the standard type 410 is: 0.15% max. carbon, 1.00% max. manganese, 1.00% max. silicon, 0.040% max. phosphorus, 0.030% max. sulphur, 11.50%

to 13.50% chromium, and remainder iron.

With comparatively close but entirely practical limitation upon the combined manganese and nickel contents' of the type 410 steel I tnd that remarkably improved qualities are obtained particularly in the matter of strength 40 under high temperature operating conditions. -'Ihese qualities are dramatically accented when my new alloy is contrasted with, say, the commercial type 422 or even the 422-M, a 422 alloy which has been modified through the addition thereto of tungsten, 'molybdenum and vanadium, all in an attempt to increaseV the high temperature ingredients carbon, chromium, molybdenum,

strength thereof. In comparison with the type 422 steel, as well as type 422-M, I lnd my'new steel to demonstrate markedly superior high temperature strength.

The steel of my invention essentially consists of the tungsten and vanadium, with remainder substantially all iron. essential, too, that the ingredients manganese and nickel which are present in the stainless steels; be limited, to value not exceeding .25% for the manganese and not exceeding .25% for the nickel and the total of the two Needless to say, the inv not exceeding .25%. The steel of'my invention thus analyzes approximately .15% to .40% carbon, 10.50% to 13.50% chromium, .25% maximum manganese, .50% maximum silicon, .25% maximum nickel, 1.00% to 3.00%

molybdenum, .20% `to .70% vanadium, .75% to 2.25%

tungsten, .25 maximum nitrogen, .10% to .60% columbium, with the sum ofnickel and manganese not exceeding .25 and remaindensubstantially all iron.

An even more preferred range of eompositionfor my steel is: about .23% to .28% carbon, .15% max. Ymanganese, :03% max. phosphorus, .03% max. sulphur, .35% max. silicon, 11.0% to 12.0% chromium, .15% max. nickel, 1.25% to 1.75%l molybdenum, 1.0% to 1.5%-tungstcn, .30% to .45% vanadium, .08% to .12%

nitrogen, .20% to .40% columbium, with sum of nickel and manganese not exceeding .25%, and ,remainder substantially all iron.

It is.

It is to be noted that the foregoing compositions represent preferred ranges. No attempt is here made to provide a broad composition range. This is largely because I find it to be the studied and intentional limitation of the combined quantities of nickel and manganese, i.e. austeniteformer s, within straight chromium, low carbon steel of this general type, which brings about the good results which I seek; fthe total quantity of manganese and nickel considered together, not exceeding .25% by weight. And the improvement in high Aterrperature strength carries over in varying degree to a number of the low chromium, low carbon stainless steels wherein austeriite-formers are maintained within controlled low limits.

It is significant that with chromium content ranging within 10.50% to about 13.50, carbon being maintained at low value, ranging from about .15% to about .40%, suflicient strong carbide-formers such as molybdenum, tungsten and vanadium to effectively combine with the carbon and prevent any free carbon to serve as an austenite-former; and finally, with the sum of nickel and manganese maintained at no greater than .25% maximum, my desired new results are dramatically displayed.

As specifically illustrative of the practice of my invention I give the composition in Table I(a) below of two steels made in the induction furnace. And in Table I(b) below I give the mechanical properties of the two steels, first at room temperatures (A) and at high temperatures (B):

TABLE I(a) vmaximum figure of .25%.

at about 2100 F. for A hr. and quenched in oil, giving In the test specimens of heat E9201 it will be seen that the ingredients nickel and manganese are maintained at combined value of .19%, i.e., well within maximum permissible limit of .25%. So also in those of heat 034080 with a manganese content of .13% and a nickel content of .10% the sum of the two is well within the permissible All specimens were heated a structure essentially martensitic, together with some ferrite. The specimens then were subjected to a temperature of about 1200 F. for 4 hours, to relieve internal stresses within the matrix. Following this, the specimens were cooled in air.

Testing was conducted at both room temperatures and at elevated temperatures. At room temperature the test specimens are seen to have ultimate tensile strengths ranging up to 178,000 p.s.i., with .2% yield strength of about 146,000 p.s.i. Elongation within 2" specimens was found to be some 12%.to 14.5% with reduction in area of 39% to 44.5%. The hardness was 387 Brinell to Rockwell 39.5.

At high temperatures rupture was had of sample E9201 at 1100 F., with loading of 60,000 p.s.i. in about 355 hours. At 50,000 p.s.i. approximately 1530 hours was required to fracture. As might well be expected, some slight decrease in strength attended higher temperatures. At 1200 F. and a loading of 30,000 p.s.i. fracture took place at 350 hours. With loading reduced to 23,000 p.s.i., 833 hours were required to fracture. Similar to the Chemical Composition of Two Steels According Present Invention rrriatomnrastorNtMowvCbN E9201-.- .2e .o1 Jole-.02o .19 11.31 .12 1.59 1.23 .4a .2e .1o 034080.-- .21 .1a 010' .021 .s4 11.36 .1o 1.58.1.00 .41 .21 .004

TABLE I(b) stress rupture characteristics are noted for specimens of turemeehanicalpropertles ofthe two stee of Table heat 034080.

[(AZ )Room tem I a (2100 for 16 hr. and oil quench +1200 F. 1er 4 hrs. and nir cool)l n tN U'rs 27Ys PWR/n.1 1m H 1 ee o. ercen p.. ar-

p.a.l. p.s.i. ElAnjZ" pgrcerit Ft. ness f .f Lbs.

178,000 146.000 12.0 39.0 Blgglell 176,600 147,200 14. 5 43.8 12-11 Re 30.5. 176,500 145,300 14515 44.6 11-12 Rc39.

B Hl h temperature ropertles-Stressrupture tests ot the two steels l( oi tubie I(a)-(2100 for M hr. and oil quench +1200 F. for 4 hrs.,

air cooDl Heat No. Temp. ot Load, Hoursto Elong.2", RJ...

p.s.i. Fracture percent Percent 60, 000 855. 1 7. 0 13. 8 50, 000 1529. 6 7. 4 12. 8 $1,000 349.6 9.2 80.5 23, 000 833. 6 12. 2 27. 5 85.000 89.2 0. 1 24.2 80,000 825.7 6.3 11.8 71,000 (Dbcontlnued at 2,014 hrs. at 2.65 total elongcreep rate 1000to2000 .000869 0340@ 1, 100 60, 000 230. 0 (Discontinued just prior to fracture to prevent Jolt) 1,100 55.000 497.0 6.5 15.7 1, 100 60, 000 1, 085. 2 5. 5 11. 8 1, 200 80. 000 232. 0 10. 0 24. 8 1,200 23,000 601.8 14.7 20.2

In hardening the steel of my invention I preferably employ a temperature of about 2100 F., this for about 16 hour, followed by an oil quench. f I observe that where hardening 'is undertaken at operating temperatures apprec1ably in excess of 2100 F., as for example 2150 F. or more, there is perhaps too much delta ferrite retained 1n the metal upon quenching. I desire, however, to retain some small quantity of delta ferrite for I feel that the presence of a small quantity thereof advantageously aects the high temperature strength of the alloy. Experimentally, I have determined that suflcient delta ferrite is retained when my preferred steel is hardened at about 2100 F. Satisfactory hardening is had within 4the temperature range of about 2050 F. to 2150' F.

A tempering temperature of about 1200 F. is preferred since I iind that in general it is advisible to temper the metal at a temperature which is slightly higher than that at which the steel is intended normally to operate. Turbine blades and the like are tempered at about 1200 F. under the assumption that they will operate under prevailing temperature of 1150 F.

The superior high temperature characteristics of my steel are dramatically illustrated by a series of tests comparing my steel with the known 'type 422 steel. The chemical analyses of my steel and the type 422 of the TABLE II prior art. This superiority assumes added signilicance when it is particularly recalled that it is the type 422-M Chemical Analyses of Comparative Samples of the Present Steel and Prior Art Types 422 and 422-M 1 From Bt/eel" for November 12, 1956, vol. 139, No. m.

TABLE III 2 Stressl Rupture Figures at 1000 F., 17100 F. arid 1200 F. for Present Steel and for Type 422 Prs. steel (Ht. 034000) Type 422 Temp., Stress,

F. p.s.t Rup. Percen* Percent Rup. Percent Per- Life, El. in R.A. Life, E in cent Hours Hours R.A.

1 35,000 50.2 5.4 24.2 30 1 80,000 825.7 03 11.8 1 70,000 13.0 18.0 00 1 00.000 301.0 14.0 55 1 00,000 235.0 1.3 23.0 73.0 1, 55, 000 507. 0 0. 5 15. s 1, 50,000 1, 030.0 5.5 11.8 31.0 19.0 70.0 1, 30,000 232.0 10.0 24.8 30.0 17.0 62.0 1, 23,000 001.8 14.7 20.2 1, 20,000 v330.0 22.0 l'10.0

The results given above, plotted on log-log scale, wherein stress in pounds per square inch are set out as a function of time required to fracture, expressed in hours, 40

this for temperatures of 1000 F., 1100 F. and 1200 F., are shown in FIG. 1 of the drawing. For the tests at 1000 F., FIG. 1 discloses that specimens of my steel sustain a load of 71,000 p.s.i. after 5000 hrs., while the type 422 steel, similarly tested at 1000 F. sustains a load of only 50,000. p.s.i., for the 5000 hr. period, a re- 4 duction of more than 20,000 p.s.i. in loading poten-tial. At 1100 F.as disclosed in FIG. l, and here the superior characteristics of my new steel are even more strikingly displayed, type 422 sustains a load of 25,000 p.s.i. for 5,000 hrs., while my new steel carries a load of 40,000 5 p.s.i. for the 5,000 hr. period. At 1200 F. the type 422 sustained a load of about 17,000 p.s.i. for 1,000 hrs. against a load of about 21,000 p.s.i. for my steel. Or, viewed from the load-life standpoint, the type 422 indicated a life of about 340 hours for a load of 20,000 p.s.i., as against a life of something over 1,000 hrs. with like load for my steel.

The advantages of high temperature properties of my steel as compared with the types 422 and 422-M are illustrated in a series of rupture curves, designated master rupture curves, presented in FIG. 2 of the drawings (sometimes known as parameter curves). Actually, the curve for my steel based upon the data given in Table II above is applied to the published curves for the types 422 and 422-M as given in Steel" for November l2, 1956, vol. 139, No. 20, as referred to above. Rupture stress in pounds per square inch, expressed in thousands, is given as a function of the temperature-time parameter. This is deined as the absolute test temperature multiplied by the sum of 20 plus the log of the time required to fracture, expressed in hours, times 10-3.

Comparison of the three curves of FIG. 2 quickly reveals that under high temperature operating conditions my new steel displays a high temperature strength substantially greater than either of the two steels of the 0 Cr Nl4 Mn Si Mo W V Gb N which has been developed in an attempt to solve the very same problem towards which my present disclosure is directed.

Upon comparing analyses of the steels set out in Table II, it is worthy to note that in the type 422 both the nickel content thereof and the manganese content are appreciably greater than both the individual and the combined limits of the steel of my invention. As to the type 422- M, the quantity of nickel closely approximates my maximum limit but the manganese appreciably exceeds that limit and the combined values of these two metals importantly exceedsthe maximum permissible limit of my steel..

It appears that the increase in strength resulting from the limitation of the combined nickel and manganese contents of my steel is attributable to an entirely different phenomenon from that imparting increased strength values to type 422-M steel, with its added tungsten, vanadium and molybdenum. For with the 422 steels (types 422 and 422-M) it is these additives, which are strong carbide-formers, which are necessary to impart even an approximation of the required high temperature strength.

In any event, it becomes apparent from the foregoing that much importance attaches to the limitation of the combined nickel and manganese contents of the modified 12% chromium steel of my invention, the two ingredients being maintained at a maximum of approximately .25%. For while straight chromium, low-carbon stainless steels have been proposed, significantly in none of these has there been any disclosure, nor realization, of the surprising phenomena attendingthe marked limitation'of total quantity of manganese and nickel.

I am by no means certain as to just why it is that high strength attends the composition of my new steel with the proposed heat treatment thereof. Nor do I know the technical'explanation involved. Perhaps it is that the combination of low nickel and low manganese tends, in straight chromium low-carbon steels, to bring about low internal stressing within the tempered martensite matrix. Perhaps validity attaches to this theory in that it has become recognized that, where internal stressing is high within the matrix of an alloy steel, particularly where the alloy is intended for high temperature service, such important internal stressing usually contributes to lowered resistance of the alloy, and this both to creep and to rupture. While I by no means desire to be bound by such proposed theory of operation, perhaps it is this limitation of manganese and nickel, with retention in the converted martcnsite of av small yet sufficient quantity of ferrite, which brings this about.

Thus it will be seen that I provide in my invention a steel in which the objects set forth above, together with many practical advantages, are successfully achieved. My

invention reduced, high temperature performance is improved. The presence of ferrite makes possible tempering to uniform stress, with retention of the essentially martensitic composition along with limited yet requisite ferrite. It has been observed that an entirely martensitic composition does not favorably respond to tempering treatment.

All these, as well as many other practical objects and advantages attend the practice of my invention.

It is apparent that once the broad aspects of my invention are disclosed, many embodiments thereof will readily suggest themselves to those skilled in the art. As well, many modifications of the embodiments here disclosed and described will likewise propose themselves. Accordingly, I intend the foregoing disclosure to be considered solely as illustrative, and not as a limitation.

I claim as my invention:

1. A'stainless steel essentially consisting of .23% to .28% carbon, .15% max. manganese, .03% max. phosphorus, .03% max. sulphur, .35% max. silicon, 11.0% to 12.0% chromium, .15% max. nickel,` 1.25% to 1.75% molybdenum, 1.0% to 1.5% tungsten, .30% to .45% vanadium, .08% to .12% nitrogen, .20% to .40% columbium, with the sum of the manganese and nickel contents not exceeding .25%, and remainder substantially all iron.

2. A stainless steel essentially consisting of about 0.25% carbon, manganese up to .25% maximum, phosphorus up to 0.03% maximum, sulphur up to 0.03% maximum, silicon up to 0.35% maximum, about 11.5% chromium, nickel up to 0.25% maximum, molybdenum about 1.50%, tungsten about 1.25%, about 0.40% vanadium, about 0.10% nitrogen, about 0.30% columbium, with the sum of manganese and nickel together not exceeding 0.25% maximum, and the remainder substantially all iron.

3. A lowcarbon, heat-hardenable stainless steel, low

in austenite-formers and which, in hardened condition displays high strengths at elevated temperatures, said steel essentially consisting of about .25 carbon, 12.0% chromium, .25 max. nickel, .25 max. manganese, with the sum of the nickel and manganese contents not exceeding .25%, .50% max. silicon, 1.50% molybdenum, 1.00% tungsten, .40% vanadium, .3% columbium, and the remainder substantially all iron.

4. A heat-hardened and tempered stainless steel essentially consisting of about .23% to .28% carbon, .25% max. manganese, .50% max. silicon, 11.0% to 12.0% chromium, .25%,max. nickel, 1.25% to 1.75% molybdenum, .30% to .45% vanadium, 1.0% to 1.5% tungsten, .25% max. nitrogen, .20% to .40% columbium, with the manganese and nickel together not exceeding a maximum of 0.25%, and the remainder substantially all iron.

5. Heat-hardened and tempered martensitic stainless steel products displaying high strength at temperatures within the approximate range of 1000 F. to 1200 F. essentially consisting of about .23% to .28% carbon, .25% max. manganese .50% max. silicon, 11.0% to 12.0% chromium, .25% max. nickel, 1.25% to 1.75% molybdenum, .30% to .45% vanadium, 1.0% to 1.5% tungsten, .25% max. nitrogen, .20% to .40% columbium, with the manganese and nickel together not exceeding a maximum of 0.25%, and the remainder substantially all iron, which products have been hardened by heat treatment and then tempered.

References Cited in the iile of this patent UNITED STATES PATENTS 2,590,835 Kirkby et al. Apr. 1, 1952 2,693,413 Kirkby et al. Nov.v 2, 1954 2,793,113 Rait et al May 2l, 1957 2,848,323 Harris et al Aug. 19, 1958 2,853,410 Lula Sept. 23, 1958 

1. A STAINLESS STEEL ESSENTIALLY CONSISTING OF .23% TO .28% CARBON, .15% MAX. MANGANESE, .03% MAX. PHOSPHORUS, .03% MAX. SULPHUR, .35% MAX. SILICON, 11.0% TO 12.0% CHROMIUM, .15% MAX. NICKEL, 1.25% TO 1.75% MOLYBDENUM, 1.0% TO 1.5% TUNGSTEN, .30% TO .45% VANADIUM, .08% TO .12% NITROGEN, .20% TO .40% COLUMBIUM, WITH THE SUM OF THE MANGANESE AND NICKEL CONTENTS NOT EXCEEDING .25%, AND REMAINDER SUBSTANTIALLY ALL IRON. 